Please try to configure your email piping email in any email client like thunderbird, outlook, apple mail, etc. If it is successfully configured in the email client then please use the same details to configure email piping.
To achive this you need to use external cron method. Go to Support > Settings > Cron Settings and select the External Cron method. You have to set cron in your hosting control panel to execute a given command every minute or set timing as per your requirement. After that go to Support > Settings > Email Piping > Other Settings > Cron Execution Time and set it as per your requirement.
The user may be directly replying to that original email which he used while creating a ticket using email piping. He should reply to the ticket email notifications which are sent to him by our plugin. If they reply to the original email then plugin does not get a ticket ID and hence the reply did not get imported into the ticket and instead creates a new ticket.